I've never heard about wormers causing positive tapeworm test
However as equisal is a test for antibodies, they can still be in the system after the tapeworms have gone.
You get a positive test. You worm and it's cleared the tapeworms. However the antibodies may not return to normal for weeks or even months. That's why you have to allow time before retesting after worming.
ETA just checked and 16 weeks between tapeworm s being killed and antibodies returning to normal